H漫画

The Gondwana Formation (GF) is a poorly understood lithological unit at the base of the Lesser Himalayan Sequence (LHS), with a poorly constrained Permian age. West of Nepal and East of Bhutan, in the Sikkim region of India, tectonics and perhaps river incision influenced the formation of a double tectonic window revealing micaceous sandstones of the GF in the core. Bounded by the Main Central Thrust (MCT) at the base, and the Ramgarh Thrust in the roof, the area has undergone a great amount of deformation resulting in a transverse antiform of the LHS. Such structures are rare in the Himalayas and one hypothesis states that these structures are the result of interaction between tectonics (Himalayan collision) and focused erosion (incision of the largest Himalayan rivers). Using ⁴⁰AR/³⁹AR dating of detrital muscovite grains from GF, the provenance of GF will be interpreted. This study will determine ages of detrital muscovite grains obtained from the footwall of the Ramgarh thrust, and use these ages to infer probable granitic and basement sources of sediments that comprise the GF. Preliminary ages suggest that the temperatures caused by Tertiary Himalayan metamorphism and tectonic burial were not high enough to reset the ⁴⁰AR/³⁹AR ages of the muscovite grains. This puts a constraint on maximal temperatures and therefore burial attained by the GF.

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Pages: 72
Supervisors: Djordje Grujic / Isabelle Coutand